This invention relates to a method of and apparatus for adding heat to molten metal.
In all forms of molten metal treatment at elevated temperatures, it is important to control the heat flow.
The first item here is to control the heat losses, expedient thermal insulation being of prime importance. This is however by no means always sufficient, and it is then necessary to add heat, preferably without at the same time adding to the melt unwanted substances.
Heat can be added through the bottom and walls of the container holding the melt, over the melt or in the melt. For practical and economic reasons, the latter method is often preferred, and is that on which the present invention is based.
It is known that an electric arc can be used, either between fixed electrodes or between a fixed electrode and the melt in order to add heat to the melt. This method results in large temperature differences between the upper and lower layers of the melt. Further, there can easily arise differences in the chemical composition of the upper and lower layers. In the upper layer, particularly near the electrode, components in the melt will evaporate whilst at the same time materials are added by the electrode, the usual occurrence being that carbon is given off by the electrode and absorbed by the melt.
Heating the melt by an electric arc thus results in gradients in temperature and in chemical composition. Achieving the desired metallurgical product requires experience, time and the analysis of samples throughout the process.
These problems would be reduced, or completely eliminated, if there were a simple method of continuously mixing the melt whilst it is being supplied with heat by an electric arc.